Metal remelting with concentrated solar power

ABSTRACT

One disclosed embodiment is a concentrated solar thermal system for re-melting recycled or scrap metal. The system includes a solar receiver configured to receive concentrated solar flux reflected from one or many reflecting surfaces to heat a quantity of the recycled metal and cause at least a portion of the recycled metal to melt. The molten metal is then passed to a solidification stage where the molten metal may be cast into any type of solid form useful for sale or the subsequent production of metal products. The solidified metal may be sold or otherwise removed from the system. In certain embodiments, heat exchange is made to occur between the molten metal and the working fluid of an electrical power generation cycle resulting in electrical power generation. Methods of remelting metal using solar thermal power and methods of generating power using a molten metal heat transfer material derived from recycled metal or scrap are also disclosed.

TECHNICAL FIELD

The embodiments disclosed herein relate generally to concentrating solar thermal technology and more particularly to methods and apparatus for remelting recycled metal with concentrated solar power and optionally using the melted recycled metal as a heat transfer material for electrical generation.

BACKGROUND

Primary metal production and recycling are well known industrial activities requiring vast amounts of energy. Particularly in metal recycling, a large fraction of the required energy usage is simply to provide heat to melt scrap metal prior to reprocessing the scrap into billets or other useful forms. The melting steps required for metal recycling are commonly performed with coal-burning reverberatory furnaces (in the case of aluminum recycling) or electric-arc furnaces (in the case of steel recycling). These processes can be inefficient. For example, reverberatory furnaces cause conversion of aluminum into slag and dross and electric-arc furnaces produce heat from electricity which is a relatively inefficient heat production method.

The embodiments disclosed herein are directed toward overcoming one or more technical limitations including but not limited to the problems discussed above.

SUMMARY OF THE EMBODIMENTS

One embodiment disclosed herein is a concentrated solar thermal system for re-melting recycled or scrap metal. The system includes a source of recycled (or scrap) metal. As defined herein, recycled or scrap metal is any metal of any type which has previously been manufactured into a product, or which is an otherwise unused by-product of a metal manufacturing process. The system includes a solar receiver configured to receive concentrated solar flux reflected from one or many reflecting surfaces to heat a quantity of the recycled metal and cause at least a portion of the recycled metal to melt. The system also includes a solidification stage receiving molten recycled metal and providing for the molten metal to be cast into any type of solid form useful for sale or the subsequent production metal products. The solidified metal may then be sold or otherwise removed from the system.

In certain embodiments, the system also includes at least one heat exchanger in fluid communication with the solar receiver which receives molten metal from the receiver and provides for heat exchange between the molten metal and the working fluid of an electrical power generation cycle. The system may include fluid or solid material conduits which provide for recycling some or all of the molten metal between the solar receiver, an optional molten metal storage system or the solidification stage. In embodiments which include an electrical power generation cycle, the system may be configured as an open-ended system where substantially all of the recycled or scrap metal input to the solar receiver is cast into a useful solid form either directly after melting, after storage or after optional heat exchange with an electrical power generation cycle.

Alternatively, certain embodiments may be operated as a periodically closed-loop system where the molten metal is passed through the solar receiver and any heat exchanger elements multiple times before being cast into a useful form and removed from the system.

Certain embodiments include preprocessing of the recycled or scrap metal prior to input to a solar receiver. For example, recycled scrap metal may be shredded prior to input to the receiver or shredded and then compressed into a billet of desirable shape before input to the receiver.

Other embodiments include methods of remelting metal. Remelting method embodiments utilize a source of recycled or scrap metal as defined above, which may be shredded or compressed into a suitable shape. The metal is then loaded into a solar receiver configured to receive concentrated solar flux causing at least a portion of the metal to melt. The molten metal is then cast into a solid form with a casting machine or other solidification stage. The solid form may be of any shape including but not limited to ingots, billets, sheets, wire, grains or other forms. The solid may then be removed from the system, sold or remanufactured into a useful product.

Other embodiments comprise a method of generating electricity. Electricity generation methods also utilize a source of recycled or scrap metal which may be loaded into a solar receiver and melted as described above. The melted metal functions as a heat transfer material and after heating is caused to undergo heat exchange with the working fluid of a electricity generation cycle. Energy transferred to the working fluid may then be used to drive one or more turbines to generate electrical power. The melted metal heat transfer material may be solidified into a useful solid form and removed from the system as described above or recirculated to the solar receiver for additional heating. In certain embodiments, additional heat exchange between the working fluid and metal heat transfer material occurs during or after the solidification process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a thermal solar powered recycled or scrap metal remelting system.

FIG. 2 is a schematic diagram of an alternative thermal solar powered recycled or scrap metal remelting system.

FIG. 3 is a schematic diagram of a thermal solar powered recycled or scrap metal remelting system with recuperative input pre-heating.

FIG. 4 is a schematic diagram of a thermal solar powered recycled or scrap metal remelting system with an associated power generation cycle.

FIG. 5 is a schematic diagram of an alternative thermal solar powered recycled or scrap metal remelting system with an associated electrical power generation cycle.

DETAILED DESCRIPTION

Unless otherwise indicated, all numbers expressing quantities of ingredients, dimensions, reaction conditions and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”.

In this application and the claims, the use of the singular includes the plural unless specifically stated otherwise. In addition, use of “or” means “and/or” unless stated otherwise. Moreover, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements and components comprising one unit and elements and components that comprise more than one unit unless specifically stated otherwise.

The embodiments disclosed herein include concentrated solar thermal systems and methods for remelting metal including but not limited to recycled or scrap metal. In addition, concentrated solar power (CSP) systems and methods are disclosed which feature the use of recycled metal as a heat transfer material (HTM) which undergoes a solid-liquid phase change. The term “heat transfer material” is used herein instead of the more commonly used “heat transfer fluid” because in certain stages of the described systems, the recycled or scrap metal HTM is moved, stored and utilized as a non-fluid solid. In certain embodiments detailed below, the system is open-ended. Therefore, metal is input to a solar receiver to be melted and then later solidified into a useful form for sale, remanufacturing or otherwise taken away from the solar recycling system. In other embodiments, the system is operated in partially or periodically closed-loop manner with scrap metal being input to the system and moved through a heat transfer cycle more than once before being cast into a useful form and removed from the solar thermal facility.

FIG. 1 is a schematic diagram of a system 100 which is configured to melt recycled metal and cast the metal into a solid form for sale or subsequent manufacturing processes. The system 100 is therefore an open-ended system. Recycled metal, illustrated by cans 102 is shredded by shredder 104 prior to melting. It is important to note that the recycled metal input to the system 100 may be of any type including but not limited to aluminum, steel, copper, iron, chromium or other metals. The source of the metal may be aluminum cans, cars, structural steel, byproduct (scrap) metal formed during other metal fabricating processes or any other source of metal. Selected pre-processing steps such as shredding the recycled metal in shredder 104 may include any physical or chemical process necessary or advisable to prepare the metal for melting in a solar receiver 106.

In the FIG. 1 embodiment, the system 100 includes a compressor 108 which operates to compress shredded recycled metal into billets 110 which are sized and shaped to be input into the solar receiver 106. The system also includes a mechanical conveyance illustrated as the chain driven billet lift 112. The billet lift serves to move a series of billets 110 from a cold storage unit 114 to the solar receiver 106.

At the solar receiver 106, the recycled metal billets are subject to illumination with concentrated solar flux which causes some or all of the metal to melt into a liquid. The molten recycled metal may then flow, for example in conduit 116, to a casting machine 118 for casting into an ingot, bar, billet, sheet or other form which may be sold were used to manufacture products. Prior to casting, the molten recycled metal may be stored in a hot storage tank 120 which may provide thermal storage useful for electricity generation as described in detail below.

In the system embodiment 100 of FIG. 1, the solar receiver 106 is shown on top of a concentrating solar thermal tower. A tower-based receiver may be advantageous in the described implementation because a tower-based receiver associated with a large field of heliostats can be configured to achieve the high operational temperatures sufficient to melt metal. It is important to note however that other concentrating solar power receiver and system configurations may be suitable for use with a metal recycling/melting system.

The system 100 of FIG. 1 illustrates a conventional casting machine 118 as a solidification stage configured to form the molten recycled metal into a solid which is suitable for sale or subsequent manufacturing purposes. The system could alternatively be implemented with other types of solidification stages as are known in the metal fabrication or metal processing arts.

FIG. 2 is a schematic diagram showing an alternative system 200 which is configured to utilize shredded recycled or scrap metal directly at the input of a solar receiver 106 in particular, recycled or scrap metal 102 is shredded in the shredder 104 as described above. The shredded metal is then loaded into a cold storage tank 202 and subsequently conveyed to an inlet to the solar receiver 106 with a material transport system. The illustrated material transport system includes a chain driven bucket lift 204. The bucket lift 204 dumps or mixes shredded metal into a quantity of previously melted recycled metal in a slurry mixing chamber 210. The hot slurry is then input to the solar receiver 106 where additional solar flux causes some or all of the newly added shredded metal to melt.

As shown in FIG. 2, the liquid metal conduit 206 leading from the solar receiver 106 is provided with a return loop 208 between the outlet of the receiver 106 and the slurry mixing chamber 210. Downstream from the return loop, the molten recycled metal may be processed as described above in FIG. 1 with a casting machine 118. The slurry mixing chamber 210 and return loop 208 of the system 200 provide for the shredded recycled metal input into the solar receiver to be substantially preheated, reducing the quantity of solar flux required to complete the metal melting process in the solar receiver 106. FIG. 3 shows an alternative system 300 and method for utilizing a preheating step. In particular, system 300 is similar to 100 described above with the addition of a recuperated heat stream 302 which transfers heat from the casting machine to a recuperative preheater 304 which preheats billets 110 prior to loading the billets into the solar receiver 106.

The recuperated heat stream 302 may use any suitable heat transfer fluid, water steam or heat transfer oil for example, to move heat from the casting machine to the recuperative preheater 304. Accordingly, the casting machine 118 will typically be provided with suitable heat exchanger elements which facilitate heat exchange between the molten or solidified recycled metal in the casting machine 118 and the heat transfer fluid in the recuperated heat stream 302. The transfer of heat from the casting machine 118 to the recuperated heat stream 302 can accelerate the casting process by cooling the molten or solidified metal and also accelerate the initial melting process by preheating the input metal prior to the solar receiver. Therefore, use of a recuperated heat stream 302 and recuperative preheater 304 can provide for relatively enhanced throughput.

As noted above, heat from the molten or solidifying recycled metal may be utilized to improve system throughput or efficiency. Alternatively, as shown in FIG. 4, a system 400 may be designed to use a portion of the heat transferred to the recycled metal during the melting process to generate electricity. System 400 is similar in many respects to the system 200 of FIG. 2. The casting machine element 118 however, is implemented with a heat exchanger which provides for heat exchange between the molten and or solidified recycled metal and the working fluid of an electric power generation cycle 401. In the embodiment illustrated in FIG. 4, the system 400 includes a primary heat exchange stage which may be implemented with a direct contact heat exchanger 402. In the primary heat exchange stage, heat is exchanged between molten recycled metal flowing in conduit 206 and the working fluid flowing in working fluid conduit 403. The system 400 also includes a secondary heat exchange stage 404 at the casting machine, where heat is exchanged between the electrical power cycle working fluid flowing in conduit 406 and the solidifying (or solid) metal in the casting machine 118. Energy transferred to the working fluid may be used to power one or more turbines 408 to generate electrical power. In the FIG. 4 embodiment, the recycled metal may be removed from the system, sold or processed into a product after being cast into a useful form, such as billets 410.

System 400 is therefore substantially open-ended and does not include significant thermal storage. System 500 of FIG. 5 may, on the contrary, be operated periodically in a closed-loop fashion. In particular, molten recycled or scrap metal flowing in conduit 116 from the solar receiver 106 may selectively be routed to the casting machine 118 through heat exchangers 402 and 404. Thus, as described above, the system 500 may be operated in an open-ended fashion where heat from the melted recycled metal provides a thermal energy source to operate an electrical power generation cycle 401. An optional hot buffer and storage tank 120 may be provided which will allow the casting machine 118 and heat exchangers 402, 404 to operate for a period of time after sufficient solar flux is unavailable to melt additional metal, at night for example.

Alternatively, the system 500 may be operated periodically in a closed loop fashion. For example, molten recycled metal may undergo primary heat exchange with the working fluid of the electric power generation cycle 401 in the primary heat exchanger 402 and then re-circulated to the receiver in return conduit 502 for additional heating. Electricity may thus be generated for a period of time without removing billets 410 from the system, increasing the efficiency of electrical power generation operations. The optional hot buffer and storage tank 120 may be used to allow the system to generate electricity for a period of time after sufficient solar flux is unavailable to melt metal flowing through the receiver, at night for example. System 500 therefore provides an operator with the opportunity to favor power generation, or metal recycling operations or a combination of both, based upon the needs of the power grid, energy prices, recycled metal prices and other considerations which may change on an hourly, daily, weekly or other periodic or random basis.

As noted above, systems 400 and 500 may be used to re-melt recycled or scrap metal and/or to generate electricity. When used to generate electricity the recycled metal functions as a HTM which is a solid-liquid phase change material (PCM). Certain CSP systems and methods featuring the use of solid-liquid phase change material (PCM) as a heat transfer material (HTM) are described in co-owned and co-pending PCT patent application PCT/US2012/045425 entitled; “Concentrating Solar Power Methods and Systems with Liquid-Solid Phase Change Material for Heat Transfer” the content of which application is incorporated herein for all matters disclosed therein. Other related CSP systems and methods are described in a United States provisional patent application entitled “Flow Control Systems and Methods for a Phase Change Material Solar Receiver” and “Apparatus and Methods for Recovering heat Expelled During Metal Casting” which applications are incorporated herein for all matters disclosed therein.

As defined herein a solid-liquid phase change material is a material which exists in a solid phase at cooler operating temperatures but melts to a liquid phase at hotter operating temperatures. One benefit of utilizing a phase change material as the HTM of a CSP system is the high energy density realized by exploiting the latent heat as well as the sensible heat of a suitable HTM. The energy storage density of a suitable HTM can typically be doubled by exploiting the latent heat storage of a phase change transition.

The foregoing systems may be implemented with various alternative receiver designs. In any embodiment, the solar receiver is configured to heat the recycled or scrap metal HTM and cause at least some solid HTM to melt. The disclosed systems also include one or more heat exchangers in fluid and thermal communication with the solar receiver and receiving liquid HTM directly or indirectly from the receiver. The heat exchanger(s) may be of any type or any level of sophistication needed to provide for heat exchange between the liquid HTM and an electrical power generation cycle working fluid. The heat exchanger(s) also provide for the cooling and solidification of liquid HTM in conjunction with heating the working fluid.

The heat exchanger elements and other subsystems are, for technical convenience described and shown in the figures as simple schematic elements. All elements of a commercial system would be implemented with more complex apparatus.

The disclosed systems also include material transport systems providing for the transportation of solid HTM from the outlet of the heat exchanger to the solar receiver for reheating. Thus, some or all of the HTM undergoes a thermal cycle including a solid to liquid phase change as solar energy is applied to the HTM and a liquid to solid phase change as energy is exchanged with a working fluid.

The embodiments disclosed herein are not limited to any specific type of heat exchanger, power generation block or any specific working fluid. The high operating temperatures achievable with certain types of metal HTM facilitate use with higher temperature thermodynamic power production cycles for example a supercritical CO₂ (s-CO₂) Brayton cycle. All types of power block will include one or more turbines which are caused to rotate by the heated working fluid to generate electricity. The power block 416 typically include some or all of the following power block elements: turbines, compressors, condensers, expansion stages, recuperators, heat exchangers and associated pipes, ducts, valves and controls.

The heat exchanger elements described herein may include separate HTM and working fluid conduits such that heat is exchanged between the HTM and working fluid without physical mixing of the HTM and working fluid streams. Alternatively, a direct contact heat exchanger may be utilized where liquid metal HTM interacts directly into the working fluid of the power cycle. In a direct contact heat exchanger, direct physical contact between the HTM and the working fluid heats the working fluid as the liquid metal HTM is solidified.

Appendices A, B and C attached hereto contain additional disclosure supporting the disclosed embodiments and directed to additional and supplemental embodiments.

Various embodiments of the disclosure could also include permutations of the various elements recited in the claims as if each dependent claim was a multiple dependent claim incorporating the limitations of each of the preceding dependent claims as well as the independent claims. Such permutations are expressly within the scope of this disclosure.

While the invention has been particularly shown and described with reference to a number of embodiments, it would be understood by those skilled in the art that changes in the form and details may be made to the various embodiments disclosed herein without departing from the spirit and scope of the invention and that the various embodiments disclosed herein are not intended to act as limitations on the scope of the claims. All references cited herein are incorporated in their entirety by reference. 

1. A concentrated solar thermal system for remelting recycled metal comprising: a source of recycled metal; a solar receiver configured to receive concentrated solar flux to heat a quantity of the recycled metal and cause at least a portion of the recycled metal to melt; and a solidification stage receiving molten recycled metal from the solar receiver, the solidification stage providing for the molten recycled metal to be cast into a solid form.
 2. The concentrated solar thermal system for remelting recycled metal of claim 1 further comprising a heat exchanger in fluid communication with the solar receiver, the heat exchanger receiving molten recycled metal, and providing for heat exchange between the molten recycled metal and a working fluid of an electric power generation cycle.
 3. The concentrated solar thermal system for remelting recycled metal of claim 1 further comprising a fluid conduit system providing for transportation of a first portion of molten recycled metal from an outlet of the solar receiver to an inlet of the solar receiver, the fluid conduit system further providing for transportation of a second portion of the molten recycled metal to the solidification stage.
 4. The concentrated solar thermal system for remelting recycled metal of claim 3 further comprising: a shredder receiving recycled metal at a shredder input and providing shredded recycled metal at a shredder output; and a material transport system providing for the transportation of shredded recycled metal to the solar receiver input.
 5. (canceled)
 6. The concentrated solar thermal system for remelting recycled metal of claim 1 further comprising a compressor providing for the forming of recycled metal into a compressed form for input into the solar receiver.
 7. (canceled)
 8. The concentrated solar thermal system for remelting recycled metal of claim 1 further comprising: molten metal storage providing for the storage of molten recycled metal received from an output from the solar receiver; a recuperative heat transfer conduit providing for the transfer of heat energy from at least one of the solidification stage; the solar receiver outlet or the molten metal storage; and a recuperative pre-heater providing for the pre-heating of the recycled metal prior to input into the solar receiver.
 9. The concentrated solar thermal system for remelting recycled metal of claim 1 further comprising molten metal storage providing for the storage of molten recycled metal received from an output from the solar receiver, wherein the molten metal storage provides for thermal energy storage using the molten recycled metal as a thermal energy storage medium.
 10. The concentrated solar thermal system for remelting recycled metal of claim 9 further comprising a heat exchanger in fluid communication with at least one of the solar receiver or the molten metal storage, the heat exchanger receiving molten recycled metal from at least one of the solar receiver or the molten metal storage, and providing for heat exchange between the molten recycled metal and a working fluid of an electrical generation power generation cycle.
 11. The concentrated solar thermal system for remelting recycled metal of claim 10 wherein the heat exchanger comprises a direct contact heat exchanger providing for physical contact between the molten recycled metal and the working fluid.
 12. The concentrated solar thermal system for remelting recycled metal of claim 10 wherein the heat exchanger comprises a multiple stage heat exchanger comprising at least a primary stage where heat exchange occurs between molten recycled metal and the working fluid and a solidification stage where heat exchange between the heat transfer material and the working fluid causes solidification of the molten recycled metal.
 13. (canceled)
 14. A method of recycling metal comprising: providing a source of recycled metal; heating a quantity of the recycled metal in a solar receiver configured to receive concentrated solar flux causing at least a portion of the recycled metal to melt; and casting the molten metal into a solid form in a solidification stage receiving molten recycled metal from the solar receiver.
 15. (canceled)
 16. The method of claim 14 further comprising: shredding the provided recycled metal at a shredder input; and transporting shredded recycled metal to the solar receiver input.
 17. (canceled)
 18. The method of claim 14 further comprising compressing the received recycled metal into a form for input into the solar receiver.
 19. (canceled)
 20. The method of claim 14 further comprising: storing molten recycled metal received from an output from the solar receiver in a molten metal storage system; transferring heat energy in a recuperative heat transfer conduit from at least one of the solidification stage; the solar receiver outlet or the molten metal storage; and pre-heating the provided recycled metal prior to input into the solar receiver using the transferred heat energy.
 21. An electrical power generation method comprising: providing a source of recycled metal; heating a quantity of the recycled metal in a solar receiver configured to receive concentrated solar flux causing at least a portion of the recycled metal to melt; exchanging heat between the molten recycled metal and a working fluid of a power generation cycle; generating electrical power with a turbine driven by energy provided by the working fluid; and casting the molten metal into a solid form in a solidification stage. 22-24. (canceled)
 25. The method of claim 21 further comprising compressing the received recycled metal into a form for input into the solar receiver.
 26. (canceled)
 27. The method of claim 21 further comprising: storing molten recycled metal received from an output from the solar receiver in a molten metal storage system; transferring heat energy in a recuperative heat transfer conduit from at least one of the solidification stage; the solar receiver outlet or the molten metal storage to a recuperative pre-heater; and pre-heating the provided recycled metal in the recuperative pre-heater prior to input into the solar receiver using the transferred heat energy.
 28. The method of claim 27 further comprising exchanging heat between the molten recycled metal and a working fluid of an electrical power generation cycle in a heat exchanger in fluid communication with at least one of the solar receiver or the molten metal storage.
 29. The method of claim 28 further comprising exchanging heat in a direct contact heat exchanger providing for physical contact between the molten recycled metal and the working fluid.
 30. The method of claim 29 further comprising exchanging heat in a multiple stage heat exchanger comprising at least a primary stage where heat exchange occurs between molten recycled metal and the working fluid and a solidification stage where heat exchange between the heat transfer material and the working fluid causes solidification of the molten recycled metal. 